Item decorator which can apply offsets to first and last items

ItemOffsetCornerItemsDecoration.kt

package lt.markmerkk

import android.content.Context
import android.graphics.Rect
import android.view.View
import androidx.recyclerview.widget.RecyclerView
import androidx.recyclerview.widget.RecyclerView.ItemDecoration
import lt.ermitazas.base.dpToPx

/**
 * Item decorator which can apply offsets to first and last items
 * Source: https://medium.com/@pa1pal/set-spacing-in-recyclerview-items-by-custom-item-decorator-3312cf489fce
 * Source: https://gist.github.com/yqritc/ccca77dc42f2364777e1
 */
class ItemOffsetCornerItemsDecoration(
    private val context: Context,
    private val offsetItemFirst: Offset = Offset.asEmpty(),
    private val offsetItemLast: Offset = Offset.asEmpty(),
) : ItemDecoration() {

    override fun getItemOffsets(
        outRect: Rect,
        view: View,
        parent: RecyclerView,
        state: RecyclerView.State
    ) {
        super.getItemOffsets(outRect, view, parent, state)
        val childCount = parent.adapter?.itemCount ?: 0
        val childPosition = parent.getChildAdapterPosition(view)
        when {
            childPosition == 0 -> {
                outRect.set(
                    offsetItemFirst.start,
                    offsetItemFirst.top,
                    offsetItemFirst.end,
                    offsetItemFirst.bottom,
                )
            }
            childPosition == childCount - 1 -> {
                outRect.set(
                    offsetItemLast.start,
                    offsetItemLast.top,
                    offsetItemLast.end,
                    offsetItemLast.bottom,
                )
            }
        }
    }

    data class Offset private constructor(
        val top: Int,
        val bottom: Int,
        val start: Int,
        val end: Int,
    ) {
        companion object {
            fun asEmpty(): Offset {
                return Offset(
                    top = 0,
                    bottom = 0,
                    start = 0,
                    end = 0,
                )
            }

            fun new(
                top: Int = 0,
                bottom: Int = 0,
                start: Int = 0,
                end: Int = 0,
            ): Offset {
                return Offset(
                    top = top,
                    bottom = bottom,
                    start = start,
                    end = end,
                )
            }

            fun Offset.withDp(context: Context): Offset {
                return Offset(
                    top = context.dpToPx(top),
                    bottom = context.dpToPx(bottom),
                    start = context.dpToPx(start),
                    end = context.dpToPx(end),
                )
            }
        }
    }
}